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United States Patent |
5,323,726
|
Olsson
|
June 28, 1994
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Method and device for controlling a multi electrode sweep
Abstract
The invention relates to a method and a device for sweeping marine mines
having a magnetic sensor by at least three electrodes (10, 11, 13) spaced
apart and tractored by a vessel (12) and behind each other, the electrodes
being provided with electric current from the vessel (12) for generating a
magnetic field in the water surrounding the electrodes (10, 11, 13), each
of the electrodes (10, 11, 13) separately being provided with electric
current of individually adjustable strength. The invention is
characterized by varying in time the current strength of the current fed
to the electrodes between positive and negative limits with intermediate
zero passages to separate the time for zero passage of the current to at
least one of the electrodes (10, 11, 13) from the time for zero passage of
the current to the rest of the electrodes (10, 11, 13).
Inventors:
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Olsson; Thord M. (Bjarred, SE)
|
Assignee:
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SA Marine AB (Landskorna, SE)
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Appl. No.:
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910309 |
Filed:
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July 21, 1992 |
PCT Filed:
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January 22, 1991
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PCT NO:
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PCT/SE91/00039
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371 Date:
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July 21, 1992
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102(e) Date:
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July 21, 1992
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PCT PUB.NO.:
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WO91/10587 |
PCT PUB. Date:
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July 25, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
114/221R; 102/402; 114/242 |
Intern'l Class: |
B63B 021/00 |
Field of Search: |
114/221 R,244,242,313,322,330,312
102/402,407
340/850,851,852
|
References Cited
U.S. Patent Documents
2397209 | Mar., 1946 | Schaelchlin et al. | 114/221.
|
2937611 | May., 1960 | Schaelchlin et al. | 114/221.
|
3060883 | Oct., 1962 | Herbst et al. | 114/221.
|
3707913 | Jan., 1973 | Lee | 102/18.
|
3826215 | Jul., 1974 | Dyjak | 114/221.
|
3946696 | Mar., 1976 | Lubnow | 114/221.
|
4562789 | Jan., 1986 | Bornhofft et al. | 114/221.
|
4627891 | Dec., 1986 | Gibbard | 204/1.
|
4697522 | Oct., 1987 | Groschupp et al. | 102/402.
|
Foreign Patent Documents |
0205887 | May., 1986 | EP | .
|
0338901 | Apr., 1989 | EP | .
|
0366522 | Oct., 1989 | EP | .
|
977801 | Jul., 1970 | DE | .
|
8903788 | Mar., 1989 | WO | .
|
Other References
Mine Countermeasures at Defendory '86.
|
Primary Examiner: Mitchell; David M.
Assistant Examiner: Avila; Stephen P.
Attorney, Agent or Firm: Mason, Jr.; Joseph C., Smith; Ronald E., Hansson; Anders
Claims
I claim:
1. A method for sweeping marine mines of the type having a magnetic sensor,
comprising the steps of:
spacing at least three electrodes apart from one another;
tractoring said at least three electrodes behind a vessel in longitudinally
spaced relation to one another;
supplying each of said at least three electrodes with electric current from
said vessel for generating a magnetic field in water surrounding said at
least three electrodes;
separately supplying each of said at least three electrodes with electric
current of individually adjustable strength;
varying said electric current in time between positive and negative limits
with intermediate zero passages to separate the time for a zero passage of
the electric current to at least one preselected electrode of said at
least three electrodes from the time for a zero passage of the electric
current to the other than said at least one preselected electrode.
2. The method according to claim 1, further comprising the step of
supplying electric current to the electrode closest to said vessel in
offset phase relation to the electric current to the electrode arranged
most distant from said vessel.
3. The method according to claims 1 or 2, further comprising the step of
varying the strength of the electric current while maintaining a
predetermined relationship between the electric current to the electrode
closest to said vessel and the electric current to the electrode arranged
most distant from said vessel.
4. The method of claims 1 or 2, further comprising the step of setting the
difference in time between zero passages of the strength of the current of
the electrode closest to said vessel and the strength of the current to
the electrode most distant from said vessel to a preselected time that is
below one fourth of the time interval between two zero passages of one of
the currents.
5. The method of claims 1 or 2, further comprising the steps of providing a
first electrode, a second electrode and a third electrode in sequence
behind said vessel substantially along a straight line, said first
electrode arranged closest to said vessel, and adjusting the current of
said first electrode and the current of said third electrode to a
predetermined relationship considering the size of said electrodes and the
distance therebetween, and adjusting the current of a center electrode to
a value adequate to provide predetermined propagation characteristics of
the magnetic field generated by said electrodes.
6. A vessel-towed device for sweeping marine mines of the type having a
magnetic sensor, comprising:
at least three electrodes towed by said vessel in spaced, longitudinal
alignment with one another and said vessel;
a power supply means arranged on said vessel for supplying current of
individually adjustable strength to said electrodes;
said power supply means being connected to control means for time
coordinated control of the current of the electrode closest to said vessel
and to the electrode most distant from said vessel.
7. The device according to claim 6, wherein said power supply means
includes two generators separately connected to said control means and
said electrodes for supplying electric current to said electrodes.
8. The device according to claim 6, further comprising:
a transformer connected to a generator on said vessel;
said transformer forming a part of said power supply unit;
at least a first and a second controlled current rectifier, each of which
has two output terminals;
a first output terminal of said first current rectifier being connected to
a first electrode arranged closest to said vessel;
a second output terminal of said first current rectifier being connected to
a first output terminal of said second current rectifier;
said first output terminal of said second current rectifier being connected
to a second electrode arranged behind said first electrode;
a second output terminal of said second current rectifier being connected
to a third electrode arranged behind said second electrode; and
said current rectifiers being separately operatively connected to said
control means.
9. The device according to claim 6, further comprising:
at least two DC current generators;
each of said generators having two output terminals;
a first output terminal of said first DC current generator being connected
to a first electrode arranged closest to said vessel;
a second output terminal of said first DC current generator being connected
to a first output terminal of said second DC current generator;
said first output terminal of said second DC current generator being
connected to a second electrode arranged behind said first electrode;
a second output terminal of said second DC current generator being
connected to a third electrode arranged behind said second electrode; and
said DC current generators separately being operatively connected to said
control means.
10. The device according to claims 6, 7, 8, or 9, further comprising:
said control means including a central unit;
a memory unit operatively connected to said central unit;
driver means operatively connected to said central unit; and
said driver means being connected to said power supply means.
Description
The present invention relates to a method and a device for sweeping marine
mines having a magnetic sensor using at least three electrodes which are
spaced apart, and are tractored by a vessel and behind each other, said
electrodes being provided with electric current from said vessel for
generating a magnetic field in the water surrounding said electrodes, each
of said electrodes separately being provided with electric current of an
individually adjustable strength.
When sweeping marine mines having a magnetic sensor a magnetic field has to
be generated, said magnetic field being sufficiently strong and
sufficiently similar to a magnetic field generated by a vessel to be
regarded by the mine as a vessel target, thereby detonating the mine. For
the protection of the vessel carrying out the mine sweeping it is
desirable to limit the magnetic field of such a strength to an area safely
distanced from the mine sweeping vessel, so as to prevent a mine detonated
by said magnetic field from damaging said mine sweeping vessel.
A sweeping operation must fulfil two primary demands. A first demand is to
make mines having a low sensitivity detonating even if they are displaced
a large distance in the transverse direction of the track of the vessel
and thereby being actuated by a comparatively weak magnetic field from the
sweep. A second demand is that mines having a high sensitivity shall not
be triggered within a certain security zone surrounding the sweeping
vessel. These claims are partially conflicting because a strong magnetic
field required to achieve said first demand hampers the achievement of
said second demand. Furthermore, the characteristics of the magnetic field
generated by the sweep should be such that it is identified by the mine as
a magnetic field generated by a target vessel, even if the mine is
provided with means for analyzing surrounding magnetic fields.
The method of sweeping marine mines having a magnetic sensor by means of an
electrode sweeping arrangement comprises the following steps. Two or more
electrodes are placed in the water and tractored by one or several
vessels. The electrodes are supplied with electric current from said
tractoring vehicle, the current in the cables and through the water
generating the desired magnetic field.
U.S. Pat. No. 2,937,611 discloses a system in sweeping marine mines by
means of a plurality of vessels, each vessel being provided with a pair of
electrodes. The system provides a pulsating magnetic field between the
electrodes. U.S. Pat. No. 2,397,209 relates to a system in mine sweeping
according to which a pulsating magnetic field is provided between two of
the electrodes tractored by the vessel. A more complicated system in mine
sweeping is disclosed in U.S. 3,946,696. The system comprises two
electrodes, a controlled current generator, and a magnetic field sensor.
There is also included a control system controlling the current through
the electrodes dependant on the magnetic field in the vicinity of the mine
sweeping vessel. By measuring the magnetic field adjacent to the mine
sweeping vessel the desired safety of the mine sweeping vessel can be
obtained. SE,A, 8704069-7 relates to a method and a device in sweeping
marine mines having a magnetic sensor. At least three electrodes are
tractored spaced apart behind a vessel and behind each other, and said
electrodes separately are provided with electric current of individually
adjustable strength from said vessel for generating a magnetic field in
the water surrounding said electrodes.
Another simple constructive step to increase the protection of the mine
sweeping vessel without any impairing of the desired mine sweeping
capabilities is to extend the mine sweeping arrangement behind the vessel.
However, practical problems in dealing with long cables limit the length
of the mine sweeping arrangements.
The magnetic field from a vessel moving normally and passing a mine varies
in each position by time and can be regarded as combined by components in
three directions of the co-ordinates in space. In each direction the
magnetic field varies in such a way that during some moments the value of
said magnetic field is zero. The moment of these so-called zero passages
do not coincide in said three directions, a fact which is used by
"intelligent" mines to avoid firing caused by a mine sweeping arrangement
as described above, said zero passages of said arrangements coinciding in
said three directions.
An object of the present invention is to accomplish a method for sweeping
marine mines which are fired magnetically, said method fulfilling the
above described demands. The object is accomplished by providing said
generated magnetic field propagation characteristics having a sufficiently
weak magnetic field in the vicinity of the mine sweeping vessel and a
magnetic field varying in time according to the steps set out in claim 1.
The invention will be described in more detail by means of an embodiment by
reference to the accompanying drawings, in which
FIG. 1 schematically shows a prior art three electrode sweep,
FIG. 2 is a graph showing the field propagation of the three electrode
sweep according to FIG. 1,
FIG. 3 schematically shows a three electrode sweep according to the present
invention,
FIG. 4 schematically shows an embodiment of the three electrode sweep
according to the present invention,
FIG. 5 schematically shows an alternative embodiment of the three electrode
sweep according to the present invention,
FIG. 6a and FIG. 6b are graphs showing how the current in two electrodes
varies in time, and
FIG. 6c-e are graphs showing how the magnetic field varies in a position in
the water in three directions in time.
As mentioned initially two partly contradictory demands have to be
accomplished when sweeping mines. The magnetic field must be sufficiently
strong to detonate mines in an area as large as possible. Using the mine
sweep according to FIG. 1 a field propagation according to FIG. 2 can be
accomplished. The mine sweep comprises a first electrode 10, a second
electrode 11 and a third electrode 13. The current I.sub.1 in said third
electrode 13 and the current I.sub.3 in the second electrode 11 are
provided through a control and regulating unit 14 in turn being provided
with electric current from a not shown power supply means. From FIG. 2 it
is also clear how said electrodes are arranged on line behind a tractoring
vessel 12, said third electrode 13 being arranged closest to said vessel,
and said second electrode 11 being the last electrode. The lines of flux
indicate the magnetic field in terms of nT. The width of an area covered
by a magnetic field 100 nT strong is just above 400 m. Most mines will
identify 100 nT as vessel target. The flux density allowed in the vicinity
of the mine sweeping vessel varies depending on different factors, but
should preferably be limited to 5 nT.
A crucial factor of the field propagation characteristic of a three
electrode sweeping arrangement is the relationship between the current
I.sub.1 in the front electrode 13 and the current I.sub.3 in the rear
electrode 11, the distances between electrodes 10, 11 and 13, and the way
the supplied current (and thereby also the magnetic field) varies in time.
The distances between said electrodes are indicated in FIG. 2, and the
relationship between I.sub.1 and I.sub.3 is 1, i.e. the strength and
direction of current I.sub.1 are equal to the strength and direction of
current I.sub.3. Each of the electrodes in the electrode sweeping
arrangement is supplied separately with current, and the current in each
electrode is controlled individually. To accomplish a magnetic sweep
having the desired propagation characteristics the arrangement is first of
all made with an appropriate consideration to the types of electrodes, the
types of cables and the distances between the electrodes. Starting with
these fundamentals the desired relationship between said current I.sub.1
in said front electrode 13 and said current I.sub.3 in said rear electrode
11 is determined. Said currents I.sub.1, I.sub.2 and I.sub.3 are then
adjusted to appropriate values so as to achieve the desired current
relationship.
FIG. 3 shows an embodiment in principle of a device according to the
invention. A power supply means 15 provides through separate means each
electrode in the sweeping arrangement with an individually controllable
current. To make possible a desired adjustment of the current supply to
said electrodes with regard to time, and thereby also the magnetic field,
in three space co-ordinate directions said power supply means 15 is
operatively connected to a control means 23 comprising a central unit 21
and a memory unit 22 in which control data to said central unit for
accomplishing any desired sequencies of varying magnetic field is stored.
In a simple embodiment said control means 23 comprises a conventional
mechanical timer, and in a further developed embodiment said central unit
21 comprises a computer and said memory unit comprises electronic memory
chips and in some cases memories on magnetic media. The method according
to the invention is described in more detail below with reference to FIG.
6.
FIG. 4 shows schematically an embodiment of the device according to the
invention. The power supply means 15 comprises a first generator 16,
providing said rear electrode 11 with the current I.sub.3, and a second
generator 17 providing said front electrode 13 with the current I.sub.1.
Said generators also comprise a common terminator which is connected to
said center electrode 10 and through which said current I.sub.2 is
supplied. Control signals generated in said control means 23 are amplified
in two driver means 24, 25. If AC generators are used rectifiers are
provided between said generators and said electrodes. Controlled
rectifiers are preferably used to make possible an adjustment of the
current strength. The flow direction of currents can of course be
reversed.
In the embodiment shown in FIG. 5 the power supply means comprising two
controlled current rectifiers 18; 19 is connected to a generator existing
on said vessel 12 through a transformer 20.
All electrodes and cables are of conventional type.
The method according to the invention will now be described in more detail
with reference to FIG. 6a-e. FIG. 6a is an example of how the current
I.sub.1 in said front electrode 13 is varied in time by said control means
23, and FIG. 6b shows a corresponding variation of the current I.sub.3 in
said rear electrode 11. As is clear form FIG. 6a and FIG. 6b the zero
passage of I.sub.3 is displaced T.sub.0 s in relation to the zero passage
of I.sub.1. The period of the variation of the current I.sub.1 is referred
to as T, and T.sub.0 should preferably be less than or equal to T/4. The
variation of said current I.sub.1 and I.sub.3 results in a variation also
of the magnetic field. FIG. 6c-e show the variation of the magnetic field
in an arbitrary position in the three space co-ordinate directions x, y
and z. As a result of the displacement T.sub.0 also the zero passages of
the magnetic field in said three directions are displaced, and it is
ensured that the generated magnetic field to a high extent corresponds to
the magnetic field of a vessel.
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